1. Field of the Invention
The present invention relates to an image-scanning apparatus and image-scanning method therefor for multi-color photomechanical color printing, and more particularly, to an image-scanning apparatus and an image-scanning method therefor which require a simple operation for accurate image-scanning.
2. Description of the Related Art
In the conventional multi-color photomechanical process, a drum scanner and a magnification-measuring instrument have been used for image-scanning. An image-scanning method employing the aforesaid conventional equipment will be explained below.
An original is fixed on a scanner drum (transparent cylinder) by means of an adhesive tape. After that, the drum is rotated and the original is read by the sensor.
Separately from the above, an image of the original is projected on a layout sheet through a magnification-measuring
instrument and thereby the then projection magnification is obtained. Or, the original and the layout sheet are measured by means of a scale for calculating the magnification. The layout sheet, in this case, means the one on which a frame is precisely drawn based on an instruction paper which is given to the photomechanical process for instructing the finished size and layout. A layout sheet mentioned hereinafter includes not only a layout sheet itself but also an original instruction sheet and a copy thereof.
For each of a plurality of originals pasted on the drum, the magnification obtained in the aforesaid way is set from the operation portion for the drum scanner.
When it is necessary to fix an original according to the angle instructed by the layout sheet, the original is positioned relative to the corresponding frame on the layout sheet and an angle formed between the reference line o the layout sheet and one side of the original is measured by the use of a protractor. Or, data of an angle is obtained from a magnification measuring instrument.
When fixing an original on a drum, the original is to be positioned so that an angle formed by a reference line on the drum and a reference side of the original may be the same as the measured angle. Or, the original is to be fixed on the drum after aligning the reference side of the original to the reference line of the measured angle drawn on a transparent sheet.
How to set a highlight and a shadow point of an original will be explained next.
An operator first determines, through the visual check, the highlight portion on the original fixed on the drum, then he turns the drum by hand so that a reading head may coincide with the determined highlight portion, and he measures the density thereof. At the same time, he measures the density on each of a shadow portion and a medium gradation point in the same manner.
The relation between the magnification/angle thus obtained and the original is based on the memory of an operator.
When fixing an original, close attention should be paid not to damage the expensive drum and original. Since the original belongs to a customer, it is not allowed to be damaged.
In order to increase the speed for reading an original, the drum needs to be rotated at high speed, which causes an apparatus to be large in size.
Further, in addition to the drum scanner main body the original needs to be handled by another apparatus for the measurement of magnification, which increases the risk, of damaging the original. Further, because the originals are handled without being covered, the distinction among plural originals is difficult.
For the original requiring the magnification which is extremely different from that of the previous original, it is necessary to change a drum. After fixing an original on the drum, each original requires its own magnification. In that case, there is no way but to rely upon the memory of an operator when ascertaining which measured magnification corresponds to which original, which has increased the probability of an error.
In the measurement of an angle, there has also been a disadvantage similar to that in the aforesaid magnification measurement.
Angle setting is done on a transparent cylinder, but it is difficult to measure an angle on the cylindrical surface, which tends to lower accuracy of measurement. The method employing a transparent sheet is time-consuming and there is a fear that the reading accuracy is adversely affected by the insertion of a sheet.
When setting a highlight and a shadow point, it is necessary to rotate the drum by hand and align a reading head, which is complicated.
The invention has been devised in view of the problems mentioned above, and its object is to realize an image scanning apparatus and method therefor wherein a magnification and an angle may be measured and set through a simple operation, thereby, a plurality of originals can be scanned efficiently.